Comments

It's syslog format: RFC 5424. The bit in angle brackets is the priority, which I believe is always 134 = local0.info in the logs that Fastly sends. The next bit is the timestamp, followed by the hostname of the machine that generated it. Next is the "app name" field, which is the name that you configured for the syslog endpoint in fastly. Finally, the thing in brackets is a process ID, which is unlikely to be meaningful to anyone outside Fastly.